Calcolare
[math]int \\sin^4 dx[/math]
[math]\\sin^4x=\\sin^2x \cdot \\sin^2x=\\sin^2x \cdot (1-\\cos^2x)=[/math]
[math]=\\sin^2x-\\sin^2x \cdot \\cos^2x=\\sin^2x-(\\sinx \cdot \\cosx)^2=\\sin^2x-(1/2 \cdot 2\\sinx\\cosx)^2[/math]
=
[math]\\sin^2x-1/4 \cdot \\sin^2(2x)=1/2 \cdot (1-\\cos2x)-1/4 \cdot 1/2 \cdot (1-\\cos4x)=3/8-1/2 \cdot \\cos2x+1/8\\cos4x[/math]
per cui
[math]int\\sin^4xdx=int(3/8-1/2 \cdot \\cos2x+1/8\\cos4x)dx=3/8x-1/4 \cdot \\sin2x+1/32 \cdot \\sin4x+K[/math]